This invention relates generally to medical diagnostic apparatus and methodology and more specifically relates to X-ray scanning apparatus and methodology of the type associated with computed tomography.
Within recent years, much interest has been evidenced on the part of medical diagnosticians in the field now widely known as "computed tomography." In a typical procedure, an X-ray source and detector apparatus are positioned on opposite sides of the portion of the patient which is intended for examination. In early prior art these paired elements are made to transit across the body portion to be examined while the detectors measure the X-ray absorption at the plurality of transmission paths defined during the transit process. Periodically as well, the paired source and detector means are rotated to a different angular orientation about the body and the transit process repeated. A very high number of absorption values may be yielded by procedures of this type and the relatively massive amounts of data thus accumulated are processed by a digital computer which cross-correlates the absorption values to thereby derive absorption values for a very high number of points (typically in the thousands) within the section of the body being scanned. This point by point data can then be combined to enable reconstruction of a matrix (visual or otherwise) which constitutes an accurate depiction of the density function of the bodily section examined. The skilled diagnostician, by considering one or more of such sections, can often diagnose various bodily ailments such as tumors, blood clots, etc.
Later developments in the computed tomography field are demonstrated in the copending application of John M. Pavkovich and Craig S. Nunan, Ser. No. 643,894, filed Dec. 23, 1975 and entitled "Tomographic Apparatus and Method for Reconstructing Planar Slices From Non-Absorbed Radiation," and in the copending application of John M. Pavkovich entitled "Apparatus and Method for Reconstructing Data" filed Dec. 23, 1975 under Ser. No. 643,896. Both of these applications are assigned to the same assignee as is the present application.
The apparatus disclosed in the last cited applications utilizes a fan beam source of radiation coupled with application of a convolution method of data reduction with no intervening reordering of fan rays, to thereby eliminate the errors and delay in computation time which would otherwise be involved in such reordering. The radiation source and detector means are positioned on opposed sides of the portion of the patient being examined and these elements are made to rotate through a revolution or portion thereof while the detectors measure the radiation absorption at the plurality of transmission paths defined during the rotational process.
In a typical apparatus embodiment of the Pavkovich et al type of apparatus, an assembly is provided which is rotatable about an axis extending along a central opening defined therein, together with means for positioning the bodily portion to be examined within a central opening so that the axis of assembly rotation is perpendicular to a thin, generally planar section of the body portion being scanned. A source of penetrating radiation, i.e., of X-rays or gamma rays is mounted on the assembly toward one side thereof a provides radiation in the form of a fan beam. Means are provided for rotating the assembly so that the fan beam impinges upon the bodily portion at a plurality of incident directions. Detection is enabled by means positioned on the assembly opposite the source, which thus detects non-absorbed radiation proceeding laterally along the section.
In general, computed tomography apparatus of the foregoing type has found its principal application to examination of bodily structures or the like which are in a relatively stationary condition. For example, currently available computed tomographic apparatus yields tomographic images of the beating human heart which suffer from degradation because of cardiac motion.